This invention relates generally to power generation, and more specifically, to methods and apparatus for assembling solid oxide fuel cells.
At least some known power generation systems use fuel cells to produce power. A fuel cell is an electrochemical device that converts chemical energy produced by a reaction directly into electrical energy. Known fuel cells typically include an anode, also known as a fuel electrode, a cathode, also known as an oxidant electrode, and an electrolyte. Such fuel cells are electrochemical devices, similar to batteries, which react fuel and oxidant to produce electricity. However, unlike batteries, fuel such as hydrogen and oxidant such as air are supplied continuously to the fuel cell such that it continues to produce power so long as such reactants are provided.
A fuel cell produces electricity by catalyzing fuel and oxidant into ionized atomic hydrogen and oxygen at, respectively, the anode and cathode. The electrons removed from hydrogen in the ionization process at the anode are conducted to the cathode where they ionize the oxygen. In the case of a solid oxide fuel cell, the oxygen ions are conducted through the electrolyte where they combine with ionized hydrogen to form water as a waste product and complete the process. The electrolyte is otherwise impermeable to both fuel and oxidant and merely conducts oxygen ions. This series of electrochemical reactions is the sole means of generating electric power within the fuel cell. It is therefore desirable to reduce or eliminate any mixing of the reactants, as such mixing would result in a different combination such as combustion which produces no electric power and therefore reduces the efficiency of the fuel cell.
Individual fuel cells produce power at low voltage, typically less than about 1 Volt per cell. The cells are therefore typically assembled in electrical series in a fuel cell stack to produce power at useful voltages. To create a fuel stack, an interconnecting member is used to connect the adjacent fuel cells together in electrical series. In such an arrangement, fuel flows at a substantially equal flow rate to each of the fuel cells. As a result, the failure of a single fuel cell may cause the failure of the entire fuel stack.
To enable fuel stacks to continue to operate after a fuel cell fails, at least some known fuel stacks include a plurality of valves which are magnetically actuated from external to the cell to restrict fuel flow to the failed cell. However, actuating such valves will limit fuel flow to affected cells without isolating them electrically from the other cells, and as such, may severely limit the continued operation of the fuel cell stack. In at least some other known fuel cell stacks, a conductor is inserted within the failed fuel cell to short-circuit the cell such that the fuel cell stack may be operable with the remaining fuel cells. However, because at least a portion of the stack must be disassembled to insert the conductor, the fuel cell stack can not be operated during the insertion of the conductor. Furthermore, returning the stack to a safe working and operating temperature may shorten the useful life of the stack due to thermal cycling damage.